Backflow preventers are valve assemblies that have long been used to prevent a pure, safe drinking water source to become contaminated with liquids from undesirable sources through cross connection of the drinking water supply system with a liquid system that might be or become degraded, polluted or otherwise unsafe. Typical situations in which cross connections may present hazards to drinking water supplies include any connections of city drinking water supply systems to process water systems of industrial buildings, steam boilers, pressure steam cookers, irrigation systems, and fire protection systems. City and county building codes and other government regulations typically require the use of a backflow preventer whenever such cross connections are present.
In the past, typical backflow preventers have consisted of a single spring-loaded check valve in the water supply line, perhaps between a pair of gate-type shutoff valves. However, modern building codes now require backflow preventers to include a pair of independently spring-loaded positive check valves connected in tandem between a pair of shutoff valves. One such check valve serves as a backup in case the other should fail. Modern codes also typically require that the check valves be replaceable and repairable while in-line, that is, without shutting down the system. To complicate matters, many building codes now require the upgrading of older buildings to include sprinkler systems This in turn necessitates the installation of backflow preventers in the fire protection system water lines to such buildings to prevent backflow into city water supply lines.
Codes that require the replacement of single check valves with double check valve backflow preventers have necessitated building owners to undertake major replumbing. The existing single check, valve and its associated gate valves must be removed, and the supply line cut to provide space to accommodate a pair of single check valve assemblies connected in series between a pair of gate valves. This involves the installation of four separate valve assemblies and their interconnection to each other. Moreover, separate access for repair and replacement must be provided in the valve housings for each separate check valve assembly.
Even in new construction, although not requiring expensive replacement of existing lines, installation of double check valve preventers is difficult. The double check valve backflow preventers when assembled are large, long and cumbersome. Installation involves interconnecting a first gate valve assembly, a pair of separate check valve assemblies, and a second gate valve assembly, and the connection of the opposite ends of that assembly to the water service line.
A typical single check valve assembly is the Ames Model DCV shown in a brochure published by Ames Company, Inc. of Woodland, Calif. A typical double check valve backflow preventer is the Ames Company Model DC shown in the same brochure. The spacing between the gate valves must be twice as great when a double check valve backflow preventer of the aforementioned Ames type is used instead of a single check valve, thereby requiring the aforementioned substantial replumbing when a double check preventer must replace a single check valve. Other, similiar types of double check valve backflow preventers are illustrated in a brochure published by Cla-Val Co., Backflow Preventer Division, of Newport Beach, Calif. They are designated as Models RP-1, D, 27 and 16. Still another double check valve backflow preventer assembly is shown in a brochure published by Febco Division of Johns-Manville Company, designated as the Model 805.
It has been suggested that the two check valve assemblies of a double check valve backflow preventer can be combined in a single unitary valve body for connection between a pair of gate valves, as shown for example in a two-page advertising brochure published by Hersey Products, Inc., Water Meter & Controls Group of Dedham, Mass. such assembly being designated the Hersey No. 2. The aforementioned Febco, Cla-Val and Ames companies have also produced double check valve backflow preventer assemblies incorporated in a single valve body. See, for example, the 3/4-2 inch size of the Model 805 Febco, the Models RP-2 and D-2 of Cla-Val, and the Model RP of Ames, all as shown in the aforementioned advertising materials. None of the indicated double check backflow preventers combined in a single valve body reduce to any substantial extent the overall length of the body as compared to such valves in which each check valve is housed in its own separate body. Furthermore, all such double check preventers require a separate access opening for each check valve. Thus, known double check preventers housed in a single valve body are substantially as long and cumbersome, and as difficult to install, access and service, as such preventers in which each check valve is housed in its own separate valve body. In addition, existing double check preventers housed in a single valve body still require connections to separate gate valve housings at either end of the assembly In effect, existing double check preventers housed in a single valve body have most of the disadvantages of such preventers housed in separate valve bodies.
Accordingly, there is a need for a double check valve backflow preventer assembly which can be retrofitted into an existing liquid supply line to replace a single check valve without having to remove the gate valves at either end of the assembly and portions of the supply line to accommodate the double check preventer assembly. There is also a need for a double check backflow preventer assembly which incorporates gate valve housings as part of the assembly within a single valve body. Finally, there is a need for a double check preventer which provides easy in-line access to both check valves for repair or replacement when needed.